1. Technical Field
Various embodiments relate to methods and systems for controlling a hybrid vehicle.
2. Background Art
Hybrid-Electric Vehicles (HEVs), in general, employ a combination of an internal combustion engine and an electric machine operable as one of a motor and a generator based on the desired operating state. The engine and the electric machine may be arranged in series, parallel, and/or split configurations. For example, a conventional parallel hybrid powertrain in an HEV has both an engine and an electric machine operable as a drive motor or generator. The engine is mechanically coupled to the driving wheels, such that torque from the engine, the electric machine motoring, or a combination of the two propels the vehicle. When vehicle power demands are low, the engine may turn the electric machine as a generator to recharge the battery pack, as well as provide the necessary torque to propel the vehicle. Regenerative braking is commonly used for recharging a battery pack.
In a hybrid vehicle, a fast engine transient caused by the fast engine response typically adversely affects the fuel combustion efficiency. The fast engine transient could be a torque transient, power transient, speed transient, or the like. The engine operates under non-optimum settings that require additional fuel compared to that used during operation under stoichiometric conditions, for producing the same torque. The decreased fuel efficiency caused by the use of additional fuel is mainly due to fuel enrichment of the mixture being injected into the engine. For example, an engine in an HEV during an engine transient may produce an increase of one percent of torque using an additional ten percent of fuel with respect to stoichiometric operation.
Engine fuel injection is mainly determined based on the measured air mass combined with compensation using transient fuel amounts. On the other hand, control parameters are often ‘predicatively’ scheduled based on the rate of change of engine torque command. Many of them are designed with intentional delays with finite response time. Therefore fast engine torque command directly introduces disturbance to the air/fuel (A/F) ratio and results in other non-optimum engine settings. In the case of large A/F errors, i.e., a sufficiently high degree of enrichment, it may lead to considerable fuel losses.